关键词： hydrogen chloride   hydration structure   dynamical properties   hydrogen bond   acid dissociation   proton transfer   simulation   QMCF  

摘要： An ab initio quantum mechanical charge field (QMCF) molecular dynamics simulation has been performed to study the structural and dynamical properties of a dilute aqueous HCl solution. The solute molecule HCl and its surrounding water molecules were treated at Hartree-Fock level in conjunction with Dunning double-zeta plus polarization function basis sets. The simulation predicts an average H-Cl bond distance of 1.28 angstrom. which is in good agreement with the experimental value. The H(HCl)center dot center dot center dot O(w). and Cl(HCl)center dot center dot center dot H(w), distances of 1.84 and 3.51 angstrom were found for the first hydration shell. At the hydrogen site of HCl, a single water molecule is the most preferred coordination, whereas an average coordination number of 12 water molecules of the full first shell was observed for the chloride site. The hydrogen bonding at the hydrogen site of HCl is weakened by proton transfer reactions and an associated lability of ligand binding. Two proton transfer processes were observed in the QMCF MD simulation, demonstrating acid dissociation of HCl. A weak structure-making/breaking effect of HCl in water is recognized from the mean residence times of 2.1 and 0.8 ps for ligands in the neighborhood of Cl and H sites of HCl, respectively. (C) 2009 Wiley Periodicals. Inc. J Comput Chem 31: 1785-1792, 2010

关键词： heat treating   shaping   superalloys  

摘要： Wire specimens, d = 0.1 mm, made of Ti-(50.6-50.8)at.%-Ni alloy were exposed to thermo-mechanical treatment (TMT), thus making the samples straight and providing them with high superelasticity (epsilon(se)). It was established that the most effective method of TMT is annealing with deformation at 500 and 300 A degrees C. The optimum mode of treatment was used in the research of mechanical fatigue of alloys with high superelastic properties. Two stages characterizing the alloy behavior under mechanical cycling were found out: failure accumulation and fracture. It was shown that the duration of the cycles is determined by the value of the preset deformation (sigma(set)) in relation to the deformation on the plateau-shaped area. The results of low-cycle fatigue of the alloys under investigation were processed by means of the method of least squares. The equations of prognosis of longetivity at the preset level of deformation are presented.

关键词： Mechanical milling   Crystalline oxides   Phase transformation kinetics  

摘要： This work investigates the kinetics of the anatase-to-rutile phase transformation of TiO2 powders during ball milling. Two elementary stages are observed, namely the transformation of anatase to the TiO2 II phase and of this latter to rutile. Such consecutive reactions were studied under inelastic impact regimes. Based on a suitable modeling of transformation kinetics, the fraction of powder processed on average at each collision was estimated. The mass of powder involved in phase transformation and microstructural refinement processes at each collision was then worked out by a systematic variation of the powder charge inside the reactor. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

关键词： caval vein   fluid resuscitation   septic shock   severe sepsis   mechanical ventilation  

摘要： Early optimization of fluid status is of central importance in the treatment of critically ill patients. This study aims to investigate whether inferior vena cava (IVC) diameters correlate with invasively assessed hemodynamic parameters and whether this approach may thus contribute to an early, non-invasive evaluation of fluid status. Thirty mechanically ventilated patients with severe sepsis or septic shock (age 60 +/- 15 years;APACHE-II score 31 +/- 8;18 male) were included. IVC diameters were measured throughout the respiratory cycle using transabdominal ultrasonography. Consecutively, volume-based hemodynamic parameters were determined using the single-pass thermal transpulmonary dilution technique. This was a prospective study in a tertiary care academic center with a 24-bed medical intensive care unit (ICU) and a 14-bed anesthesiological ICU. We found a statistically significant correlation of both inspiratory and expiratory IVC diameter with central venous pressure (p = 0.004 and p = 0.001, respectively), extravascular lung water index (p = 0.001, p < 0.001, respectively), intrathoracic blood volume index (p = 0.026, p = 0.05, respectively), the intrathoracic thermal volume (both p < 0.001), and the PaO2/FiO(2) oxygenation index (p = 0.007 and p = 0.008, respectively). In this study, IVC diameters were found to correlate with central venous pressure, extravascular lung water index, intrathoracic blood volume index, the intrathoracic thermal volume, and the PaO2/FiO(2) oxygenation index. Therefore, sonographic determination of IVC diameter seems useful in the early assessment of fluid status in mechanically ventilated septic patients. At this point in time, however, IVC sonography should be used only in addition to other measures for the assessment of volume status in mechanically ventilated septic patients. (C) 2010 Elsevier Inc.

关键词： AC power supply   DRAM   energy-aware systems   energy harvesting   integrated circuits   low-power design   scaling   self-timed   power-on reset  

摘要： Passive energy harvesting from mechanical vibration has wide application in wearable devices and wireless sensors to complement or replace batteries. Energy harvesting efficiency can be increased by eliminating AC/DC conversion. A test chip demonstrating self-timing, power-on reset circuitry, and dynamic memory for energy harvesting AC voltages has been designed in 180 nm CMOS and tested. An energy scalable DSP architecture implements FIR filters that consume as little as 170 pJ per output sample. The on-chip DRAM retains data for up to 28 ms while register data is retained down to a supply voltage of 153 mV. Circuit operation is confirmed for supply frequencies between 60 Hz and 1 kHz with power consumption below 130 mu W. Reaching the limits of miniaturization will require approaching the limits of power dissipation. We extrapolate from this DSP architecture to find the minimum volume required for mechanical vibration energy harvesting sensors.

关键词： Deposition rates  

摘要： Using a Hull cell with a rotating cylindrical electrode (RCE), the effect of the hydrodynamic conditions on the deposition rate and its micro- and macrodistribution and the composition and microhardness of the cobalt-tungsten coatings deposited from a citrate electrolyte containing cobalt sulphate (0.2 mol/l) and sodium tungstate (0.2 mol/l) at pH - 6.7 and the solution temperature of 60 degrees C in the Re numbers range of 0 - 3000 is examined. It is shown that the hydrodynamic deposition conditions have no effect whatsoever on the surface roughness, but they slightly influence the electrolyte's throwing power. The correlation between the intensity of the hydrodynamic flows, the deposition rate (due to the current efficiency's increase), and the composition of the coatings (along with their distribution over the surface) is established. It is shown that certain modes of the process at a high deposition rate make it possible to reach a high uniformity of the coating's composition with a high tungsten content, which results in obtaining the maximum surface microhardness.

关键词： E. coli O157:H7   Mechanically-tenderized beef   Modeling   Kinetics  

摘要： A kinetic study was conducted to investigate the growth of Escherichia coli O157:H7 in mechanicallytenderized beef meat (MTBM) inoculated and internalized with a cocktail of 5 rifampicin-resistant (Rif(r)) or 3 arbitrarily selected wild-type strains of the bacteria. The storage was conducted at 5, 10, 15, 20, 25, and 37 degrees C. No growth was observed at 5 degrees C and the growth was minimal at 10 degrees C. Above 15 degrees C, a sigmoid trend was observed for all growth curves. Three primary growth models (modified Gompertz, Huang, and Baranyi) were used to fit the growth curves. A new Belehdradek-type secondary model was found more suitable than the traditional Ratkowsky model for describing the temperature dependence of growth rate. The statistical analysis suggested that both bacterial strains and primary growth model affect the determination of growth rates (at alpha= 0.05), with Rif(r) strains growing 10-20% slower than the wild-type strains. While there was no significant difference between the growth rates estimated by the modified Gompertz and Baranyi models, and between those of Huang and Baranyi models, the rates estimated from the Gompertz model were significantly higher than those estimated from the Huang model. The temperature dependence of growth rate of E. coli 0157:H7 in MTBM was described by both a new Belehdradek-type rate model and the Ratkowsky square-root model. While the theoretical minimum growth temperatures determined by the Ratkowsky square-root model ranged from 1.5 to 4.7 degrees C, more realistic values, varying from 6.64 to 8.76 degrees C, were estimated by the new rate model. For the Baranyi model, the average h(0) value was 2.06 +/- 0.74 and 2.15 +/- 1.14 for Rif(r) and wild-type strains of E. coli O157:H7, respectively. For the Huang and modified Gompertz models, the inverse of square-roots of lag phases was found proportional to temperature, making it possible to estimate the lag phase duration from the growth temperature. The r

关键词： 微机电系统   滑动膜阻尼   分子动力学   仿真模拟  

摘要： 本论文主要是研究在微电子机械系统（MEMS）中空气滑动膜阻尼效应对微谐振器件影响。微电子机械技术在过去的二十多年里发展非常迅速，出现了很多种微机电器件和系统，其中有一大类是利用微机械结构在固有频率处所具有的优良振动性能来工作的。缩小微机械结构与电极之间的间隙是降低驱动电压的有效方法。但是当微机械振动结构和电极之间间隙缩小到一定程度时，空气分子阻尼对微机械振动结构的能量损失影响非常显著。\n 正确预测滑动膜阻尼对于MEMS器件设计是至关重要的。当气压很低时，气体连续介质模型不再适用，只能采用分子动力学方法。基于自由分子流基础上，本文提出了一种高计算效率的分子动力学算法，可以用来计算平动和振动的滑动膜阻尼。该方法以气体分子速度分布函数生成每一分子的初始速度，通过分别单独计算每一气体分子在一个单位时间内与器件碰撞获得的动量增量，得到一个单位时间内气体分子总体动量增量，从而计算器件滑动膜阻尼系数。与已有的模型结果对比表明，本文算法具有良好的精度，而且计算量是可以接受的。

关键词： Grain boundary   Mechanical behavior   Molecular dynamics  

摘要： For materials at nano-scale, the influence of interfaces is amplified due to the increased fraction of atoms located at or near interfaces. The role of several kinds of defects (point vacancies, line vacancies and cracks) during the deformation of both Cu/Cu and Cu/Al interfaces, which are used as model systems of homogeneous and heterogeneous metal interfaces respectively, is explored using molecular dynamics simulations and the embedded-atom method. Some defect topologies are found to improve, instead of degrade, certain properties (e.g. fracture strain) of a bi-crystal interface system. In some cases of a defective interface, the nucleation of partial dislocations is observed. [ABSTRACT FROM AUTHOR]

关键词： 2-Mercaptobenzothiazole   Decatungstate salts   Photodegradation   UV light   Oxygen   Photocatalysis  

摘要： The photochemical degradation of a benzothiazole derivative, 2-mercaptobenzothiazole (MBT) has been studied in aqueous solution in the presence of a polyoxometalate (POM): sodium decatungstate salts Na4W10O32 (DTA). In aerated conditions, the photodegradation rate of MBT clearly increased in the presence of DTA by a factor six when compared with the direct photolysis with k(MBT) = 0.25 h(-1) and t(1/2)(MBT)= 2.8 h. For the total comprehension of the degradation mechanism, the oxygen influence has been investigated. Oxygen appeared essential for DTA regeneration, its absence induced a three times inhibition of MBT disappearance and completely stopped the photocatalytic cycle. The main photoproducts were identified with LC-ESI-MS and LC-DAD techniques and using some calculations obtained by B3LYP/6-21G method in Gaussian 4.1 software. All the results allowed to propose a mechanistic pathway. Electron transfer and H atom abstraction processes involving W10O324-center dot excited state species were involved in the degradation. In the primary step of the degradation, the hydroxylation of the aromatic ring leading to four OH-MBT isomers and the formation of disulfide form of MBT were observed. For longer irradiation time, a secondary electron transfer permitted the oxidation of OH-MBT isomers and the formation of sulfoxide derivatives. For prolonged exposure (around 100 h), the complete mineralization was noticed in the presence of sodium decatungstate salts. (C) 2010 Elsevier B.V. All rights reserved.